U.S. Pat. No. 6,852,865 is directed to carbonylation of epoxides, aziridines, thiiranes, oxetanes, lactones, lactams and analogous compounds in the presence of a catalytically effective amount of catalyst having the general formula [Lewis acid]z+ {[QM(CO)x]w−}y where Q is any ligand and need not be present, M is a transition metal selected from the group consisting of Groups 4, 5, 6, 7, 8, 9 and 10 of the periodic table of elements, z is the valence of the Lewis acid and ranges from 1 to 6, w is the charge of the metal carbonyl and ranges from 1 to 4 and y is a number such that w times y equals z, and x is a number such as to provide a stable anionic metal carbonyl for {[QM(CO)x]w−}y and ranges from 1 to 9 and typically from 1 to 4. CO pressures ranging from 100 to 1000 psig are disclosed. High percentage conversions were obtained at CO pressures of 800 psig and 900 psig; these pressures require the use of a high pressure reactor.